Apparatus for connecting balanced and unbalanced networks in electrical systems



Dec. 23, 1941.

G. N.. sLEzsKlNSKY 2,267,430 APPARATUS FOR CONNECTING BALANCED ANDUNBALIANCED NETWORKS IN vELEC'IRICAI., SYSTEMS Filed July 20, 1940 2Sheets-Sheet l l 20 CAL/6R47? L /9 :mwa /6/ A NORME? APPARATUS FORC'ONNEGTING BALANCED AND UNBALANCE'D NETWORKS IN ELECTRICAL SYSTEMS DSC.23, 194- G N sLEzsKlsKY 2,267,430

Patented Dec. 23, 1941 UNITED STATES rarl orrics APPARATUS FOR CONNECTIGBLANCED AND UNBAL'ANCED NETWORKS 'IN ELEC- vTRICAL SYSTEMS `Gregory` NSlezskinsky, Dunellen, N. Y J., assigner to `Western Electric Company,Incorporated, N ew'York, N. Y., a corporation of New York y vApplicationJuly l20, 1940, Ser-iai No. 346,567 5 Claims. .(.QL 1794-1753) lized toeffect both cross-talkand/or loss meas-"1 urements involving apparatus`balanced and unbalanced with respect to ground potential.l Thus, forexample, one apparatus may be required for making such measurements inconnection with" the balanced pairs of a multiconductor cable andi*another apparatusmay -be required for making such measurements inconnection with concentric conductor transmission lines. The onemeasuring apparatus may embody an attenuating network balanced withrespect to ground po-L- tential and the other measuring Aapparatus mayinclude an attenuating network unbalanced with respect to groundpotential. Such individual measuring apparatus may involve not onlyadditional manufacturing expense Vvbut also additional shipping expense,as the apparatus may be required to effect `nfieasurements atdifferent'points in an extensive transmission system. Accordingly, thisinvention contemplates a single Aapparratus which may be balanced andunbalanced with respectto ground potential.

It is a general object of the invention to connect in an electricalsystem networks balanced and unbalanced with vrespect to groundpotential.

It is another object to connect metallically a I network of electricalelements balanced with respect to ground potential to another network of'electrical elements unbalanced with respect -to Iground potential.

It is a further object to utilize 1in measuring l apparatus a singlevattenuating network unbalanced with respect to ground potential toeffect measurements balanced and unbalanced with respect to groundpotential.

yIt is a still further object to compensate Vfor ground admittance dueto a parasitic capacitor and .parasitic capacitor conductance effect.

It is another object to connect in an electrical system networks whichare neither balanced nor v50 tain 'distance embodies an unbalanced'attenuating network v enveloped. lin an electromagnetic 'shield `suchthat `one or more parasitic capacities applies effectively this shield`to surrounding poi-nts of ground potential. Such apparatus is limitedto Aachieve unbalanced-to-ground measurements in connection withunbalanced-to- Eground apparatus which, in this case, may be representedby the concentric conductor transmission lines.

In accordance with this invention, the apparatus `mentioned in Athe nextpreceding paragraph andl involving the unbalanced attenuating networkyto4eifect unbalanced-to-ground measurements may also be employed withequal facility to accomplish balanced-to-ground `measurements which,`for example, may be made in connection with the vbalanced-to-groundpairs embodied in a multiconductor cable designed `for transmittingintelligence. In -a preferred embodiment the invention for this purposecomprises a terminal `at ground potential, switching means, and acapacitor having one side connected to i the latter grounded terminaland the opposite side applied through the switching means `to theunbalanced attenuating network such that the latter 'grounded terminalmay be `applied through `the latter capacitor lto the unbalancedattenuating network to efect balanoed-to-ground measure- -ments and maybe disconnected from Ithe unbalanced attenuating network to effectunbalancedto-ground measurements.

A feature of the invention is that it is also expeditiously applicableto signaling transmission `systems to connect effectively thereinnetworks balanced and unbalanced with `respect to ground potential. Anadditional feature involves the connection in `an `electrical system yofapparatus which is neither Vbalanced nor unbalanced-to- A ground.Another feature is that it maybe utilized with equal facility in anoscillator circuit ksuch that the output `thereof may be supplied to 'a`load balanced Aor unbalanced with respect to ground lpotential. Afurther feature relates to the @connection of a thermionic amplifier,which is inherently unbalanced with respect to `ground potential, `to abalanced conductor pair, -without the usual intermediary inputtransformer. Ac- 'cording1y, a "general feature is that normallylunbalanced lnetworks may be rendered, in accordance with thisinvention, suitable for use 'with balanced networks without disturbingthe 'balanced-to--ground condition of the latter, and therefore involvesbut a single network which is equally Aserviceable Iin both `balancedand unbalanced circuits.- A

vThe invention lwill -be readily understood from the followingdescription taken together with the accompanying drawings, in which:

Fig. 1 shows a general application of the preferred embodiment of theinvention;

Figs. 2A, 2B, 2C, 2D, 3A and 3B illustrate the invention applied toelectrical measuring apparatus:

Fig. 4 delineates the invention embodied in an oscillator system; and

Fig. 5 represents the invention for connecting a balanced conductor pairto a thermionic amplier which may be used in a television system.

In the following description the same reference numerals are employed toidentify the same elements appearing in the several figures of thedrawings.

Referring to Fig. 1, a source III of alternating current waves isapplied on leads and I2 to a network I3 which, for the purpose of thisdescription, may comprise a pair of resistance elements in series andwhose mid-point is applied to ground I4. Leads 24 and 25 connect thenetwork I3 to a network I5 which, for the purpose of this illustration,may comprise a pair of resistances disposed in series in the lead 24 anda pair of resistances disposed in bridge of the leads 24 and 25. Anelectromagnetic and electrostatic shield I6 encloses the network I5 andis effectively connected thereto by one or more parasitic capacitors I1,I1. A terminal 20, which is common to the lead 25, one side of thenetwork I5 and the shield I6, is connected by a parasitic capacitor I8to a point I9 at ground potential. It is to be understood that theparasitic capacitors I1 and I8 represent the capacitance of the shieldI6 to neighboring points at ground potential as hereinbefore mentioned.

From the foregoing it is obvious that the respective networks I3 and I5are balanced and unbalanced with respect to ground potential. Assumingfor the moment that the network I3 is connected alone to the source I0,then equal amounts of current are caused to flow through both branchesof the network I3 to the ground I4. However, as the balanced network I3is metallically connected by leads 24 and 25 to the unbalanced networkI5, then unequal amounts of current are caused to ilow through thebranches of the network I3 to the ground I4. In other words, the normalbalanced-to-ground condition of the network I3 is upset.

In accordance with this invention as exemplified in Fig. l, there isprovided an arrangement which compensates for or neutralizes the effectof the parasitic capacitor I8, and which, therefore, tends to maintainthe normal balanced-toground condition of the network I3. Thisarrangement comprises a capacitor 2| whose one side is connected to thelead 24 and the opposite side to ground 23. The capacitor 2| whosecapacitance equals substantially the capacitance of the parasiticcapacitor I8 tends to ensure that equal amounts of current will flowthrough both branches of the network I3 to the ground I4. In View ofthis arrangement, networks balanced and unbalanced with respect toground potential may be metallically'connected without undue groundcurrents, as the balanced-to-ground condition of the one network wouldbe substantially maintained.

Fig. 2A shows generally an arrangement for measuring cross-talk betweena disturbing pair 28 and a disturbed pair 29, both of which pairs arecontained in a multiconductor cable 30, and embodies a source ofalternating current waves 3| applied through an input transformer 32whose output Winding 33 is connected to the near end of the disturbingpair 28 terminated at the far end in a suitable network 34. Thedisturbed pair 29 is terminated at the near end in a network 35 and atthe far end in a network 36 across which are applied terminals 31, 31 ofa double pole, double throw switch 38. It is to be understood that boththe disturbed and disturbing pairs are balanced with respect to groundpotential.

Across the secondary winding 33 and in shunt of the disturbing pair 28is the input of an attenuating network 39 whose output is appliedthrough a shielded transformer 40 to a terminating network 21. Thelatter is applied to terminals 4|, 4| of the switch 38 whose terminals42, 42 are connected through an amplier-detector 43 to an indicator 44.The shield I6 envelops the attenuating network 39, together with theinput winding of the transformer 4I). The terminal 29, which is commonto one side of the input to the attenuating network 39 and also to oneside of the latter and to the shield I6, is connected by the parasiticcapacitor I8 to the point I9 at ground potential. It is to be understoodthat the network 21, together with the network 36, serves to terminatethe respective transformer 40 and disturbed pair 29 when the switch 38is either open or being operated to the terminals 31, 31 or 4|, 4|. Theoperation of Fig. 2A will be presently explained.

Fig. 2B shows a disturbing' coaxial conductor 58 and a disturbed coaxialconductor 5| between which cross-talk measurements may be made bysubstituting Fig. 2B between the lines X-X in Fig. 2A.

Figs. 2C and 2D illustrate respective apparatus balanced and unbalancedwith respect to ground potential and through which transmission orinsertion loss measurements may be accomplished by substituting theproper gure between either the lines Y-Y or X-X of Fig. 2A. In Fig. 2Cimpedances 52, 52 are inserted in both branches of the circuit in serieswith the balanced apparatus on both sides thereof while in Fig. 2Dimpedances 53, 53 are disposed in series in but one branch of thecircuit on both sides of the unbalanced apparatus. In addition, Fig. 2Dincludes a ground connection 49 disposed in the same lead which, ashereinbefore mentioned, embodies the common terminal 2U, Fig. 2A,connected through the parasitic capacitor |8 to the point I9 at groundpotential.

In the operation of Figs. 2A, 2B, 2C and 2D the switch 38 is initiallyactuated to the upward or calibrate position and the wave source 3| isadjusted to the proper testing frequency and voltage magnitude. Then,the switch 38 is actuated to the downward or measure position and thewave source 3| is adjusted to the proper frequency and voltagemagnitude, with the cable 30, under test, disconnected from the winding33 and the network 36, and the latter applied in shunt of the winding33. The gain of the amplifier detector 43 is now adjusted to provide acertain reading on the indicator 44. Then, the switch 38 is actuated tothe upward or calibrate position and the attenuating network 39 isadjusted until the same reading is produced on the indicator 44. Then,the switch 38 is actuated to the downward or measure position, and, withthe connections as shown in Fig. 2A, the gain of the amplier-detector 43is adjusted to provide a certain reading on the indicator 44.

Next, the :switch 3B is returned to the upward =or calibrate positionsand the attenuating'net- Work A39 'is adjusted until the certain`reading again produced on the indicator 44. The dilerence :in the`readings of the `atfi'fenuating network ES occasioned bythe two readings'represents the `cross-.talk passing yfrom `the disturbing pair 28 tothe disturbed .pair 29 Fig. 12A, Vor from vthe vdisturbing V.pair 50 tothe rdisturb'ed .pair 5|, Fig. 2B, or the transmission 'or insertionloss of the balanced :and unbalanced apparatus yshown in respectiveFigs. 2C and .'2D.

Referring to Fig. 2A, .it has been previously .pointed out that theparasitic capacitor 'I8 serves tolconnect a point |19 at :groundpotential to the terminal -Z'il which :is common to `the -shieldfl `and'to `one :sideoi the sir'iput 'circuit for the attenuating ynetwork 39fas welt as one `side ofthe latter. Therefore, the measurenfrent ofelectrical characteristics involving the unbalanced electrical apparatusillustrated in Figs. 2B and 2D will :be substantially correct while themeasurement oi electrical characteristics concerning the balancedvapparatus illustrated in Figs. 2A

and 2C will be incorrect. The error involved in f nboth 'oi the latteris occasioned by the connection of the common terminal 20 throughparavsitic capacitor :I' to the point |`9 at ground potential, vas suchconnection serves lto cause unequal currents 'to flow to yground inthebalanced andfdisturbing :conductor pair 28 of Fig. 2A, and `the balanced`ap'p'aratl'is of 2C. Thus, there `is upset the normalbalanced-'to-ground condition oi 'the "disturbing ypair 28 and'apparatus :shown :in the respective Figs. 2A and 2C.

In :accordance with this invention as exempli- -iled in :connection withFigs. 2A and 2G, there is provided an arrangement 'which compensates for=or `neutralizes the ele'ct of the 'parasitic capacitor i8, and which,there-fore, tends to maintain the normal balanced-to-ground condition-oi the conductor pair 128 and the apparatus oifFig. 2C. Accordingly,the arrangement of this .invention renders the attenuating network 39suitable for -accomplishing measurements both Awith respect to thebalanced apparatus of Figs. 2A and 2C land to the Vunbalanced `apparatusof Figs. 12B and 12D, land'compris'es as shown in Fig. 2A a 'capacitor25| 'whose :one termina-l isI connected to 1a .point 23 at ground'potential and whose opposite terminal may be applied by a single pole,single `throw switch 59 toa terminal 60 which Iis embodied in the inputlcircuit of the Iunbalanced attenuating network 39 in a side which isopposite to V.that embodying the common terminal 26 connected throughthe parasitic capacitor |58 to the point |9 at ground potential as`previously mentioned.

Y Thus, Athecapacitor 2| may be connected in thginpu't circuit df theunbalanced attenuating network 39 4by a lclosure of Ythe switch 59 toachieve measurements with the balanced apparatus of Figs. 2A and '2C andmay be removed from such input circuit by opening the switch 59 toachieve measurements with the unbalanced apparatus of Figs. 2B and 2D.The insertion of the capacitor '2| and ground Apoint '23 associatedtherewith 'in the "measuring circuit serves to cause equal amounts ofcurrent to Vflow in the several branches of either the balancedconductor .pair J28of Fig. 2A or the balanced apparatus of Fig. 2C,andhence enables the achievement of accurate measurements of the`electrical characteristics vof such balanced `apparalnis when 1theunbalanced attenuating network utilized .for this purpose. i lConsequently, 'accordance 'with the invenbe utilized to euect electricalmeasurements .involving apparatus both balanced and unbalanced withregard to ground potential.

Fig. 3A nlustrates primarily an `arrangement for measuring cross-talkbetween a disturbing 'conductor pair and a disturbed conductor pair,b'oth Ioff which are embodied in `a 'multiconductor cable, :and 4general'identical with Fig. l2 e'xcept in the respect 'that the secondarywindings of input 'transformer 65 are `so arranged that the inputs-oithe attenuator T39 land the 'disturbing- 'pair 28 are applied in seriesto the source 3| oli alternating `current Waves. The arrangement shownin Fig. V2C may also 'be substituted between the lines Y-Y vof Fig. 3A.Fig. 3A and the modification thereof vincluding Fig. 2C'are, therefore,utilized exclusively7 to achieve measurements involving apparatusbalanced with respect to ground potential.

Fig. `3`B is employed lto accomplish measurements only lin connectionwith apparatus unbalanced with respect `to ground potential and shown inFigs. 2B and 2D, and `for this purpose includes the vapparatus shown tothe right of the line Z--Z of Fig. 3A together with either Fig. y2B orFig. 2D

Vsubstituted between the lines 'X-X In Fig. 3B

the two secondary windings ofthe transformer "B5 areconnected in seriesin one side ofthe input circuit to the apparatus under test and theunbalanced attenuator39, as the parasitic capacitor connection to groundis effective 'inthe other side ofthe input circuit.

together with the 'modications thereof pointed balanced and unbalancedapparatus as mentioned hereinbefore in connection 'with Figs. 2A, 2B, 2Cand 2D.

Fig. 4 showstheinvention applied to an oscillator lll 'of any suitabletype whose output may be supplied `through an output transformer tooutput terminals 12, 12, which may be connected to either a balanced orunbalanced load, not shown, and which may be controlled by lanunbalanced attenuator 13. The output transformer 7H is enclosed inelectromagnetic and electrostatic shield 1li while thel secondarywinding of this transformer and the attenuator '13 are enveloped 'by theelectromagnetic Yshield I6. One output terminal l2 is connected l'by 'astrap lT6 to point 11 on the magnetic shield i5. This point is appliedby the parasitic capacitor I8 to the point |"9 vat ground potential. lItwill be `understood from the foregoing description that 'a yconnectionof `the terminals 12, T2 to a load balanced with Irespect to groundpotential, not shown, will cause a, ilow of unequal 'amounts fof currentthrough the branches of such load.

In accordance with this vinventiomthe effect of the parasitic capacitor.|'8` `may. be compensa-ted for `by connecting one terminal of Vavariable capacitor YBl] to the side of the output circuit embodying theother output terminal 12 and the opposite terminal to ground 8|. The`capacitor 80 may be adjusted until its capacitance equals sub.-stantially that of the parasiticcapacitor |;8. This will causesubstantially equal currents togiiow ,in the branclfies of the 4balancedload circuit, not

In gene-ral, the operation of Figs. '3B `and 3A,

"shown, applied to the terminals 12, 12'. It is'to Vput terminals 9I,`9I.

be understood that the capacitor 80 may have .associated therewith asingle pole, single throw vswitch 82 whereby the capacitor 80 may beapplied to one of the output .terminals 'I2 for a load balanced'withrespect to ground potential, not shown, and disconnected therefrom for aload unbalanced withrespect to ground potential, not

shown.

Fig. shows the invention applied to an arrangement whereby a vacuum tubeamplier 85, which is inherently unbalanced with respect to groundpotential, may be connected, Without an input transformer, to a balancedconductor pair 83 and 84 embodied in a multiconductor cable 81` andapplied across input terminals 88, 88. The latter may be connected to asuitable source of ,alternating current waves, not shown. The outputstage of the amplifier 85 is connected through an output transformer 89to a concentric conductor 90 which supplies the amplier output to out- Amagnetic shield 92 envelops the output transformer 89 while a magneticshield I6 encloses both the shield 89 and the ampliiier 85. Choke coils94, 95 and 96 preclude grounding of the shield 93 through the respectivesources of direct current voltage associated with the former andsupplying the amplifier 85. In this connection it is to be observed thatone such voltage source is applied through the choke coil 95 to theshield I 8 and to the shield 92, as will be hereinafter pointed out.

Parasitic capacitor I8, which represents the capacitance of the shieldI6 to surrounding points at ground potential, serves to connect to apoint I9 at ground potential a terminal 98 which is common to theconductor `83, one side of the input of the amplifier 85 and the shieldI6. A strap 99 connects electromagnetic and electrostatic shields I6 and92 while a parasitic capacitor |00 represents the capacitance of bothmagnetic shields I6 and 92 to the outer conductor of the concentricconductor 90. v

In accordance with the invention as applied to Fig. 5, a variablecapacitor IOI applied across the outer conductor of the concentricconductor 90 and a terminal |02, which is common to the conductor 84 andthe other side of the input of the amplifier 85, serves to neutralizethe eiect of the parasitic capacitor I00. A suitable balancing network|03 applied intermediate the common terminal I2 and grounded terminal|04 serves to neutralize the admittance of the shield I6 to groundthrough the choke coils 94, 95 and 96 and through the parasiticcapacitor I8. This amplifier, shown in its simplest form, is suitablefor use in a television system as pointed out in the Bell LaboratoriesRecord, October 1939, at page 36.

It is to be understood that while the invention is specificallydescribed to compensate for or neutralize a particular parasiticcapacitor-toground connection, itserves actually to compensate for aground admittance which includes the particular parasitic capacitortogether with the parasitic conductance effect.

Also, it is to be understood that the invention is equally applicable tomeasurements or connections involving conductors or other apparatuswhich may be neither balanced nor unbalancedto-ground. This situationwould tend to arise in those cases in which normally balanced apparatuswould possess unbalance due to manufacturing imperfections so that aconventional balanced attenuator when connected to such apparatus wouldtend to upset an anticipated balanced lor unbalanced connection. In ameasuring system this would tend to provide incorrect readings.

What is claimed is:

1. In combination, two conductor pairs extending together for a Acertaindistance, an unbalanced attenuator, a transformer having primary andsecondary windings, the primary winding being connected to the output ofsaid attenuator, a shield enclosing said attenuator and the primarywinding of said transformer, a source of alternating current waves,circuit means to connect said source to one of said conductor pairs andto the inputY of said attenuator, a common terminal connecting saidshield and said attenuator to one side of said circuit means, aparasitic capacitor eifectively applying said common terminal to a.minal of said capacitor to a side of said rstmentioned circuit meanswhich side is opposite to the side of said rst-mentioned circuit meansembodying said common terminal.

2. In combination, apparatus balanced or unbalanced with respect toground, an unbalanced attenuator, a transformer having primary andsecondary windings, the primary winding being connected to the output ofsaid attenuator, a

.shield enveloping said attenuator and the primary winding of saidtransformer, a source of alternating current waves, circuit means toconnect said source to the outputs of said apparatus and saidattenuator, a common terminal connect- Ying said shield and saidattenuator to one side of said circuit means, one or more parasiticcapacitors elfectively applying said common terminal to at least oneterminal at ground potential, indicating means, and means to connectalternately the output of said apparatus and the `secondary Winding ofsaid transformer to said indicating means; means to render saidattenuator suitable for accomplishing measurements involving saidapparatus and thereby tending to compensate for the effect of saidparasitic capacitors comprising a terminal having ground potential,switching means, and a capacitor having one terminal connected to saidlast-mentioned grounded terminal and the opposite terminal appliedthrough said switching means to the other side of said circuit meanssuch that said last-mentioned grounded terminal may be applied throughsaid last-mentioned capacitor to said circuit means for apparatusbalanced with respect to ground potential and may be disconnectedtherefrom for apparatus unbalanced with respect to ground potential.

3. In the combination according to claim 2 in which said apparatusbalanced with respect to ground comprises a pair of balanced electricalconductors extending together for a certain distance and said apparatusunbalanced with respect to ground comprises a pair of concentricconductors extending together for a certain distance.

4. In combination, apparatus which may be neither balanced norunbalanced with respect to ground, an unbalancedattenuator, atransformerhaving primary and secondary windings, the primary winding beingconnected to the output of said attenuator, a shield enveloping saidattenuator and the primary winding of said transformer, a source ofalternating current vwaves, circuit means to connect the inputs of saidapparatus and said attenuator in parallel to said source, a commonterminal connecting said rshield and said attenuator to one side of saidcircuit means, a parasitic capacitor effectively applying said commonterminal to a terminal at ground potential, indicating means, and meansto' connect alternately the output of said apparatus and the secondaryWinding of said transformer to said indicating means, and means tocompensate for the effect of said parasitic capacitor connection toground comprising a terminal having ground potential and a capacitorhaving one terminal applied to said latter-mentioned grounded terminaland the opposite terminal applied to the other side of said circuitmeans.

5. In combination, apparatus which may be neither balanced norunbalanced with respect to ground, an unbalanced attenuator, atransformer having primary and secondary windings, the primary windingbeing connected to the output of said attenuator, a shield to envelopsaid attenuator and the primary winding of said transformer, a commonterminal connecting said attenuator and said shield to ground potentialthrough a parasitic capacity, a source of alternating current Waves,circuit means to connect the inputs of said apparatus and saidattenuator in series to said source, indicating means, and means toconnect alternately the output oi said apparatus and the secondaryWinding of said transformer to said indicating means, means toneutralize the effect of said parasitic capacity connection to groundcomprising a terminal having ground potential and a capacity having oneside applied to said latter grounded terminal and GREGORY N.SLEZSKINSKY.

